1. Field of the Invention
This invention relates to catheters which are insertable into a biological conduit such as a blood vessel. More particularly, this invention relates to atherectomy catheters having flexible housings.
2. Previous Art
Atherosclerosis is a disease characterized by the presence of biological tissue such as atheroma, plaque and other material, on the interior walls of blood vessels. Such biological tissue is generally known as stenotic material. Stenotic material typically includes soft tractable material, or hardened material such as calcification. Stenotic material may be deposited throughout the vasculature and is commonly found in peripheral blood vessels that feed the arms and legs and in coronary blood vessels that feed the heart. Stenotic material may accumulate in localized regions, occluding the blood vessel and restricting blood flow. Restricted blood flow, in the coronary artery for example, can cause severe health problems including heart attacks and strokes.
Numerous ways of restoring blood flow have been proposed. Balloon angioplasty, for example, uses a balloon-tipped catheter to dilate the occluded region of the blood vessel. Laser angioplasty uses a laser to direct energy to ablate atheroma portions. Atherectomy uses a catheter having a cutter to sever and remove stenosis from an occluded portion of a blood vessel.
During an atherectomy procedure, a guidewire is first inserted into the vasculature of a patient via the femoral artery, for example. The guidewire advances through the vasculature to the stenosed region of an occluded blood vessel having a stenosed region. The catheter slides over, and along, the guidewire until the distal end of the atherectomy catheter positions adjacent the stenosis.
A typical atherectomy catheter has a work element such as a cutter and a housing with an opening. The housing attaches to the distal end of the atherectomy cutter and retains the cutter. The opening of the housing exposes the cutting blade. During use, the opening invaginates stenotic material which extends from a blood vessel wall through the opening. The cutter reciprocally advances past the opening. Each time the cutter advances, the cutter severs a small portion of the stenotic material and removes the severed material from the blood vessel wall. The severed stenotic material is urged into a storage area of the catheter by the cutter. Various catheters have a nose cone which attaches to the distal end of the housing for storing severed stenotic material.
Typically, the cutter has an arcuate cutting blade. The cutting blade rotates (or rotationally oscillates) when the cutter advances to optimize severance and removal of the stenotic material.
Although such atherectomy catheters have enjoyed widespread success in both peripheral and coronary applications, certain design limitations persist. The vasculature has tortuous regions with tight bends. Tortuous regions may be inaccessible by a catheter having a rigid housing. This inaccessibility limits the usefulness of catheters.
To facilitate insertion of atherectomy catheters into blood vessels having tight bends, catheters having flexible housings have been developed. Catheters with flexible housings are disclosed in U.S. Pat. Nos. 4,781,186, 5,226,909 and 5,312,425, the disclosures of which are incorporated herein by reference.
Flexible housings also have certain limitations. When flexed, a flexible cutter housing may interfere with the operation of an enclosed cutter. In particular, bending and flexing of a flexible housing may inhibit axial advancement of the cutter within the housing. This can also slow rotation of the cutter and limit cutting effectiveness. Interference between the housing and the cutter can dull the cutter and deform the housing.
Attempts to overcome the limitations associated with flexible catheters have manifested themselves. An example of a catheter with a flexible housing that minimizes interference with the cutter is described in commonly assigned U.S. Pat. No. 5,624,457 issued Apr. 29, 1997, the disclosure of which is incorporated by reference above. The flexible cutter relies on a moveable saddle which attaches to the cutter. The saddle guides the cutter to avoid interference between the cutter and the housing.
Saddles and other guiding assemblies which are small enough to fit in the housing of an atherectomy catheter are difficult and expensive to manufacture. Guiding assemblies can limit flexion of an otherwise flexible housing. Improved intravascular catheters are desired which are easy to manufacture. It is also desirable to have a catheter with a flexible housing which does not require an added guiding assembly to guide and direct the cutter. It is also desirable to provide a way of retaining the work element in the catheter housing which is compatible with flexible housings of various sizes and configurations. It is also desirable to provide a catheter having a flexible housing which is useful for removing stenotic deposits from blood vessels having tight bends.